This invention relates to a gas chromatograph and more particularly to the sample intake part of a gas chromatograph.
FIG. 5 shows schematically a portion of an ordinary gas chromatograph including its sample intake part. A septum 12 made of a silicone rubber material is provided at the top of a sample vaporization chamber 11 at the entrance to a column 10, and a carrier gas flow route 13 for introducing a carrier gas, a purge route 14 for discharging components generated by the septum 12 and a split route 15 for discharging a portion of the sample injected into the sample vaporization chamber 11 together with the carrier gas are each connected to the side of this sample vaporization chamber 11. A mass flow controller 16 for controlling the flow rate of the carrier gas such as He is contained in the carrier gas flow route 13, a pressure sensor 18 is contained in the purge route 14, and a control valve 19 for controlling the flow rate of the discharge gas is contained in the split route 15. Since there is hardly any gas resistance between the pressure sensor 18 and the vaporization chamber 11, the pressure detected by this pressure sensor 18 may be considered the same as the gas pressure inside the sample vaporization chamber. Thus, a control unit 22 monitors the gas pressure inside the sample vaporization chamber 11 through the pressure sensor 18 and controls the mass flow controller 16 and the control valve 19 such that this gas pressure remains constant and that the ratio of the amount of carrier gas supplied into the sample vaporization chamber 11 and that of the gas flowing into the column 10 (or the split ratio) will be kept at a specified level such as 100:1.
When a liquid sample is injected into the sample vaporization chamber 11, a needle 21 attached to a syringe 20 is inserted through the septum 12. The liquid sample which is dropped is quickly vaporized and carried into the column 10, riding the stream of the carrier gas, while an excess portion of the gas is discharged outside through the split route 15. The septum 12 is made of an elastic material such that the opening created when the needle 21 is inserted therethrough is quickly closed as soon as the needle 21 is pulled out. If its elastic property has deteriorated after a long period of use or the number of openings has increased after a large number of use, the opening ceases to be closed completely and the gas inside the sample vaporization chamber 11 may begin to leak out. If a chromatographic analysis is carried out under such a condition, the retention time which indicates the time of appearance of a peak in a chromatogram may be displaced or the peak area may become smaller, thereby making it difficult to obtain a reliable analytical result.
For this reason, the septum 12 should be replaced periodically with a new one. In general, however, it is left to the user or a supervisor in charge of the chromatograph to keep track of the time for exchanging the septum 12. Thus, it is often forgotten to put a new septum and analyses are carried out under a less than perfect condition. When an automatic injector is used to carry out automatic analyses of many samples continuously, in particular, a gas leakage is likely to happen, wasting many hours of time and precious samples.